Within TDM wireless communication systems, the transmission of voice messages is well known. In such systems, communication units (i.e., hand-held or in-car mobile radios) are assigned wireless communication resources in the form of radio frequency (RF) carrier divided by time into multiple time slots. Typically, these wireless communication resources (i.e., time slots) have relatively low bandwidths. In the present context, the term bandwidth is used to generally refer to the throughput rate at which a particular communication medium can be used to transmit information. These low-bandwidth wireless communication resources have been acceptable because voice messages typically do not require a high transmission rate to be transmitted in a timely manner, i.e., with a minimal amount of delay. Additionally, because the time needed to complete a typical voice message is generally small, it is a feature of many TDM wireless communication systems that the wireless communication resource used for a voice message is dedicated for the duration of the transmission.
Among users of TDM wireless communication systems, the need for transmission of non-voice messages, such as text and image files, often collectively referred to as data messages, is growing. Voice messages and data messages may be particularly distinguished by the relative amounts of bandwidth required to transmit them. That is, many data messages require high-throughput communication resources in order to be transmitted with minimal delay. When data messages are transmitted via low-throughput wireless communication resources, originally intended for voice messages, completion of the message transmission is often delayed. These difficulties notwithstanding, it would be useful to allow the bandwidth (i.e., throughput) of a particular transmission to be dynamically altered as needed and to allow voice and data messages to be simultaneously transmitted.
An example may best illustrates why current TDM wireless communication systems are not well suited to the proposed services described above. Consider an ambulance transporting a patient to a hospital emergency room. To provide voice communications between the ambulance and the hospital, a TDM wireless communication system allocates a wireless communication resource (i.e., time slot) in order to transmit the voice information. During the transmission of the voice information, it may be necessary to transmit a medical image of the patient's injuries to the hospital.
Using current TDM systems, the data message (medical image) must either be multiplexed with the voice message on the same wireless communication resource, or it must interrupt the voice message altogether. If multiplexed, both the voice message and the data message may be prohibitively delayed. If the voice message is interrupted, critical information between ambulance and hospital personnel may be missed.
One solution is to provide wireless communication resources having higher throughput rates. Technological advances such as linear amplifiers and improved modulation schemes may provide needed improvements, but such innovations are often expensive to develop and increase the complexity of the systems involved.
Another solution is to use multiple communication devices (e.g., dedicated radios) thereby eliminating the need for multiplexing and/or interruption. Such a solution, however, is cost prohibitive.
Yet another solution is to provide enough communication resources for each service request such that all potential throughput needs are met. Using the previous ambulance example, this would require that enough wireless communication resources be allocated at the time the voice message is begun so that additional messages, e.g., the medical image, may also be transmitted at any time during transmission of the voice message. While this solution alleviates the difficulties of excessive delay and, possibly, interruptions, it goes too far in that it assigns resources that could be put to immediate use for other users, thereby creating overall system inefficiencies.
Thus, it is shown that a shortcoming of prior art TDM wireless communication systems is the inability to dynamically allocate communication resources on an as-needed basis. Therefore, a need currently exists for a method wherein wireless communication resources may be dynamically allocated in response to changing service requirements or system capabilities.